Utilization of a hydraulic fluid to actuate a device or system is nearly as old as engineering itself. The use of hydraulics allows for the relatively easy application of a first force in one location to be transferred to a remote location, to be translated into a higher or lower force using differential area, etc. In general hydraulic actuation is often fairly well controlled either by pressure control alone or through the use of a metering configuration such as a spool valve. In most conditions these types of control are reliable and hence hydraulic actuation is relied upon in many industries.
Although actuation of devices hydraulically can be fairly well controlled under most conditions, significant changes in ambient conditions such as temperature and/or high actuation pressures can render control less reliable and can have noticeable effects on the actuation process including the volume of hydraulic fluid required for completion of the intended movement. This can be especially true in devices or systems requiring actuation pressures in the hundreds or thousands of pounds per square inch (PSI) of pressure. These kinds of conditions and systems situations can be difficult to precisely control. Since precision control is sometimes very important to a particular type of actuation and because hydraulic actuation is a likely consideration is countless applications, the art is always interested in alternatives that improve precision control.